GdipGetImageGraphicsContext 这个函数在C#中对应啥函数呢

[laviewpbt]

我以前在VB6中调用GDI+的相关函数，对索引色进行相关处理。

          GdipCreateBitmapFromScan0 ImgWizard.Width, ImgWizard.Height, ImgWizard.Stride, PixelFormat, BYVAL ImgWizard.Pointer, GdipSrcImg
            GdipCreateBitmapFromScan0 NewImgWizard.Width, NewImgWizard.Height, NewImgWizard.Stride, PixelFormat, BYVAL NewImgWizard.Pointer, GdiDestImg
            IF ImgWizard.BitCount<=8 THEN
                GdiPalette.Flags=%PaletteFlags.PaletteFlagsHasAlpha
                GdiPalette.Count=ImgWizard.PaletteSize
                CopyMemory GdiPalette.Entries(0),BYVAL ImgWizard.PaletteAddress,ImgWizard.PaletteSize*4
                GdipSetImagePalette GdipSrcImg, GdiPalette
                GdipSetImagePalette GdiDestImg, GdiPalette
            END IF
            GdipGetImageGraphicsContext GdiDestImg,Graphics     
            GdipDrawImageRectRectI Graphics,GdipSrcImg,0,0,NewImgWizard.Width,NewImgWizard.Height,0,0,ImgWizard.Width,ImgWizard.Height,2, 0, 0, 0
            GdipDeleteGraphics Graphics
            GdipDisposeImage GdipSrcImg
            GdipDisposeImage GdiDestImg

其中用到了GdipGetImageGraphicsContext 函数，并且是调用成功的。

在C#中 Graphics.FromImage却无法从索引图像中创建Graphics，这样后续的GdipDrawImageRectRectI 就无法正确使用了，请问有什么诀窍吗？